Method for inspecting a high-voltage switch while energized with operating voltage

ABSTRACT

A method is provided for inspecting a high-voltage switch unit, while it is energized with operating voltage, from a platform insulated from ground, wherein all breaks of the switch apparatus are shunted by a bypass device for the duration of the inspection after previous verification of the closed switching position, the bypass device being removed only after the closed position of the switch apparatus has been again verified.

United States Patent Inventor Adrian Werner Roth Wasserflnhweg 7, Aaran, Switzerland Appl. No. 786,599 Filed Dec. 24, 1968 Patented Aug. 10, 1971 Priority Jan, 11, 1968 Switzerland 583/68 METHOD FOR XNSPECTING A HIGH-VOLTAGE SWITCH WHILE ENERGIZED WITH OPERATING VOLTAGE 1 Claim, 3 Drawing Figs.

US. Cl 324/28,

200/48 Int. Cl 601: 31/02 Field oISearch 324/28,28

[56] References Cited UNITED STATES PATENTS 2,668,201 2/1954 Welsh .1 339/222 UX 3,103,560 10/1963 Bridges 200/48 X 3,372,334 3/1968 Renoglio et a1 324/126 3,422,213 1/1969 Peek et a1. r 174/71 X 2,600,304 6/1952 Krida r 324/28 X 3,443,223 5/1969 Kennon 1. 324/72 Primary Examiner-Alfred E. Smith Attorney-Waters, Roditi, Schwartz and Nissen ABSTRACT: A method is provided for inspecting a high-voltage switch unit, while it is energized with operating voltage, from a platform insulated from ground, wherein all breaks of the switch apparatus are shunted by a bypass device for the duration of the inspection after previous verification of the closed switching position, the bypass device being removed only after the closed position of the switch apparatus has been again verified.

PATENTED AUG] 0 I97:

METHOD FOR INSPECTING A HIGH-VOLTAGE SWITCH WHILE ENERGIZED WITH OPERATING VOLTAGE BRIEF SUMMARY OF THE INVENTION High-voltage switch apparatus must be inspected from time to time. This involves checking the switching contacts and, depending on the breaker system, also the arc-extinction medium, and replacing them if necessary. In order to permit carrying out such an inspection, the high-voltage switch apparatus must usually be isolated from the system network and grounded. The disadvantage of this inspection method is the temporary interruption of power transmission over the line concerned, which occurs mainly in end-of-the-line stations having no bypass.

According to the invention, this disadvantage can be avoided by a method for inspecting high-voltage switch apparatus, while it is energized, from a platform insulated against ground, and by bypassing, for the duration of the inspection, all breaks of the switch apparatus after having ascertained their closed state. After the inspection, the bypass devices are removed only after having again confirmed the closed state of these breaks.

A device serving for bypassing the breaks comprises a metallic link, suitably dimensioned for the passage of all currents which can occur in normal operation and also under fault conditions. I

The application of this method, in addition to the advantage of permitting inspections without interruption of power transmission, offers the additional possibility in certain cases of obviating the provision of isolating switches otherwise necessary for separating the grounded switch apparatus unit from the supply system during its inspection.

The method is particularly suited for the inspection of switch apparatus insulated against ground by solid insulating materials exclusively.

BRIEF DESCRIPTION OF THE DRAWING:

DETAILED DESCRIPTION The high-voltage circuit breaker shown in FIG. 1 is conventional and comprises switching elements located in insulator columns 1 having head housings 2 and mechanism housings 3. The columns further comprise support insulators 4, drive mechanism 5, a chassis frame 6 and rotating insulating columns 7, which form a force-locking connection between the drive and the switching elements. The leads 8 are connected to the terminals 9 of the high-voltage circuit breaker. A switching-position indicator 10 is provided in the chassis 6.

The inspection of the circuit breaker while in service is effected from a platform 11, insulated from ground, as follows:

First of all, the breaker unit is interlocked electrically and mechanically at the drive mechanism 5 in such a manner, that no undesired tripping can occur during the inspection.

For greater safety it is essential, before proceeding any further, to make a check as to whether operating current is flowing through the circuit breaker. In the simplest manner, this can be ascertained by reading the ammeter supplied by the pertinent line-current transformer. In the absence of such a current transformer, the person making the inspection can be raised to the high-voltage carrying line 8 from platform 11 (well insulated from ground and provided with a Faraday cage). After having established a metallic connection between the platform 11 and the line 8, the inspector can measure the current flowing through the circuit breaker by placing the arms of an induction-type ammeter around line 8. If the ammeter indicates a flow of current, the circuit breaker is in closed position. If no current flow can be ascertained in the lead 8, then one of the breaks must be open, or the lead carries no current for some other reason. Regardless, no power is being transmitted in this case, and the switch gear can be operated without disturbing the service.

After having made certain of the closed position of the mechanically and electrically locked circuit breaker, one may now proceed with bypassing the breaks. This step is carried out by working from mobile platform 11, insulated from ground. The platform 11 is moved to the desired position and is then connected to a conducting, high-voltage carrying part, for example head housing 2, of the circuit breaker. Thereafter, the devices 12, which bypass the individual switching elements are securely assembled, which can be done most simply by securely screwing devices 12 at the locations provided for this purpose.

The switch apparatus can now be inspected. The unit shown in FIG. 1 is a low-oil-content circuit breaker, whose arc-extinction chambers 13, after disassembly of the switching contacts can be pulled out at the top. As required, the contacts, the arc extinction medium, or the complete arc-extinction chambers can be replaced in the course of such an inspection. During the inspection, after eliminating the mechanical interlock, the breaker may also be operated manually in order to check its satisfactory operation.

After completion of the inspection, the switch assembly must again temporarily be interlocked in its ON position. Confirmation of this closed position can preferably again be obtained by means of current measuring devices. The current flowing in the bypass device 12 at the locations 14, while the bypassed switching elements are closed, amounts in the arrangement shown in the drawing, according to practical experience, to about 50 percent to 66 percent of the total current flowing in the lead 8. This current flowing at 14 can be measured either by an external induction-type ammeter or by means of a built-in ammeter. Should the total line current manifest itself in any portion of the bypass device, then the pertinent break of the apparatus must be open and should be checked again after correcting its switching position.

Now the bypass devices can be removed. This completes the work on the high-voltage energized portions of the apparatus. The platform 11, together with the person having carried out the inspection, can now be returned to ground potential.

The last step consists in removal of the mechanical and electrical interlocks from the drive 5 of the unit.

The bypass device is represented in FIG. 2. The conductor cross section must be amply dimensioned for the passage of operating and fault currents. The connectors 15 are devised in such a known manner, that they assure convenient and secur connections, e.g. by screws or plugs, to the corresponding switch apparatus.

FIG. 3 shows a bypass device, which is equipped with builtin current transformers or ammeters 16. The direct indicating ammeters permit continuous surveillance of the switching condition during the inspection.

What I claim is:

1. A method for inspecting a high-voltage switch apparatus, while it is energized with operating voltage, from a platform insulated from ground, said method comprising bypassing all breaks of the switch apparatus unit for the duration of the inspection, after previous verification of the closed switching position, and removing the bypass only after having again verified the closed position of the switch apparatus unit, said verification of the closed switching position of the breaks, prior to removal of the bypass being performed by current measurements in the lead of the high-voltage switch apparatus unit, as in the device which effects the bypass. 

1. A method for inspecting a high-Voltage switch apparatus, while it is energized with operating voltage, from a platform insulated from ground, said method comprising bypassing all breaks of the switch apparatus unit for the duration of the inspection, after previous verification of the closed switching position, and removing the bypass only after having again verified the closed position of the switch apparatus unit, said verification of the closed switching position of the breaks, prior to removal of the bypass being performed by current measurements in the lead of the high-voltage switch apparatus unit, as well as in the device which effects the bypass. 